How to make a 3 position switch return to the center position when keypress is released?
Play the "switching" animations with the action actuator in Flipper Mode. 

The animation will be played forward when the actuator is activated (e.g. when pressing and holding the keyboard button). When reaching the end frame the last pose will remain. 

When the actuator gets deactivated (e.g. via releasing the keyboard button) the animation will be player revers till the start frame.



Be aware this does not deal with the situation when you press the second button while the first one is still pressed.